Asthma is affected by increasing mortality and morbidity as well as by increasing costs due to hospitalizations and visits to the emergency room. It is mandatory to propose an accurate follow-up of asthmatic subjects so that they can live a normal life and avoid hospitalizations. Two tools can be use& 1) notification in a diary of daily symptoms; 2) serial assessment of peak expiratory flow rates and FEV1. These methods are widely suggested and interesting. However, several aspects including the compliance of asthmatic subjects with the assessment, remained to be examined. According to cross-sectional studies, serial measurement of non-allergic bronchial responsiveness is significantly related to the clinical and functional severity of asthma. Nevertheless, longitudinal studies do not show a satisfactory correlation. The reason for these discrepancies is unknow. Although other studies are needed to obtain direct information on the severity of bronchial inflammation, the current state of knowledge does not suggest that serial assessment of bronchial responsiveness is sufficiently valid to introduce its routine use in the follow-up of asthmatic subjects.